The present invention relates generally to defect inspection methods and apparatus for detecting microstructured pattern defects, contamination, and the like, by comparing an optically acquired image of an object to be inspected, and a reference image. More particularly, the invention relates to a method and apparatus for inspecting defects in a semiconductor device, a photomask, a liquid crystal, and other objects, in optical technique.
During the manufacture of a semiconductor device, a substrate (wafer) on which the semiconductor device is to be formed undergoes processing through hundreds of manufacturing process steps to become a product. In these process steps, for example, if any kinds of contamination sticking to the surface of the substrate (wafer) are found or if the nonuniformity of pattern formation between processes occurs, these undesirable events will cause pattern defects, rendering the semiconductor device defective. In addition, with the progress of pattern microstructuring, defect inspection systems for semiconductor devices are more strongly required to not only detect defects and contamination of a finer structure, but also detect the defects of interest (DOIs). At the same time, needs for classifying non-intended defects separately from various DOIs are also increasing. In order to meet these requirements and needs, various types of defect inspection apparatus including a plurality of detection optics and image-processing circuits (detection heads) to increase the number of defect species detectable using detection signals of the detection optics, and to improve defect detection performance, have come to be developed, manufactured, and sold in recent years, and are being applied to semiconductor-manufacturing equipment.
Defect inspection apparatus for semiconductor devices is used, for example, to inspect the surfaces of substrates after each process and detect any pattern defects and contamination that may have occurred during processes such as lithography, film deposition, or etching. The inspection apparatus is also used to issue a cleaning execution command for an apparatus conducting the process, and to early detect the occurrence of defectives due to the possible movement of critically defective substrates to the next or subsequent process sites.
The substrate on which the semiconductor device provided with required processing in the previous process has been semi-formed is loaded into the inspection apparatus, and the surface of the substrate (wafer) with the semi-formed semiconductor device is imaged. Defect discriminations based on acquired images are performed using such a threshold-based defect signal discrimination process as described in Patent Document 1 (JP-A-2003-83907), Patent Document 2 (JP-A-2003-98113, or Patent Document 3 (JP-A-2003-271927), and information such as the number of defects present on the substrate is output.
If the number of actually detected defects, Nt, is smaller than the preset defect detection threshold value Nc, the substrate will be directly moved to the next process site intact. Conversely if the number of detected defects, Nt, is larger than the defect detection threshold value Nc, a command for cleaning the previous process apparatus will be issued before the substrate is judged for reproducibility. The substrate, if judged to be reproducible, will be cleaned in a cleaning process and then subjected to the defect inspection process once again before being moved to the next process site.
As shown in FIG. 4, dies 401 and 401′ of the same pattern are arranged regularly on the semiconductor substrate to be inspected. Defects are discriminated by comparing images of these adjacent dies present at the same coordinate positions thereof in the die regions. In this case, defect-inspecting illumination optics based on conventional darkfield optics have employed s-polarized, p-polarized, and/or circularly polarized illumination light. One reason for this is that when only contamination present on a silicon substrate is to be inspected, the detection performance required can be obtained under both s-polarized illumination and p-polarized illumination. Another reason is that for contamination present on oxide films and other transparent films, the effects of changes in the amount of scattered light due to changes in film thickness can be reduced by using circularly polarized illumination light. Briefly, s-polarized illumination, p-polarized illumination, and/or circularly polarized illumination have sufficed to improve the detection performance of the optics with respect to the contamination existing on the substrate or films. Even for a wafer with patterns, if the pattern pitch is much the same as the wavelength of the light, defects between the patterns have been detectable without a problem.